1. Field of the Invention
The present invention relates generally to acceleration detecting systems for internal combustion engines, and more particularly, to a system for detecting an accelerating condition of an internal combustion engine on the basis of variations in intake air mass flow in an inlet channel provided to the internal combustion engine.
2. Description of the Prior Art
In an internal combustion engine equipped with an electronic fuel injection system, on the occasion of an accelerating condition thereof, a fundamental quantity of fuel, which is calculated on the strength of engine speed and engine load which varies in propotion to intake air mass flow in an inlet channel provided to the engine or depression at the inlet channel, is revised in a predetermined manner to produce a final quantity of fuel by which the fuel is injected into the inlet channel, so that the fuel supplied to a combustion chamber of the engine is increased in response to an augmentation in intake air mass flow resulting from an increase in opening degree of throttle. With such an increase in fuel in the inlet channel brought about in response to the increase in intake air mass flow, the combustibility in the accelerating condition of the engine is raised to improve the operation performance of the engine, and further fuel consumption, exhaust characteristic and so on are improved.
For revising the fundamental quantity of fuel in the accelerating condition of the engine in such a manner as mentioned above, there has been proposed a system for detecting acceleration in the engine, which comprises an air flow sensor for determining intake air mass flow in the inlet channel which varies in response to variations in opening degree of throttle corresponding to the movement of an accelerating pedal provided to the engine and producing a determination output signal corresponding to the determined intake air mass flow, means for differentiating the determination output signal from the air flow sensor to obtain the variation rate of the intake air mass flow in the inlet channel, means for comparing the value of the variation rate of the intake air mass flow with a predetermined value set for the accelerating operation of the engine, and means for finding the accelerating condition of the engine on the basis of the output of the comparing means when the value of the variation rate of the air mass flow is equal to or more than the predetermined value.
As disclosed in, for example, the Japanese patent application published before examination with the publication No. 56-135728, there has been also proposed an air flow sensor of a hot wire type for use in determination of intake air mass flow in an inlet channel of an engine. The air flow sensor of a hot wire type is composed of a platinum heating wire provided in the inlet channel and a power supply for supplying a current to the platinum heating wire so as to cause the latter to heat. The current flowing through the platinum heating wire is varied in propotion to variations in intake air mass flow in the inlet channel and the variation of the current flowing through the platinum heating wire is derived in the form of voltage variation to be a determination output. This air flow sensor of a hot wire type is superior in sensitivity to the variations in intake air mass flow in the inlet channel compared with, for example, an air flow meter of a flap type.
In the case where the air flow sensor of a hot wire type is used, when the engine is in an accelerating condition wherein opening degree of throttle .theta. is changed into a relatively large degree .theta..sub.2 from a relatively small degree .theta..sub.1 within a period from a time point t.sub.a to a time point t.sub.b, and then in a condition wherein the opening degree of throttle .theta. is held to be the relatively large degree .theta..sub.2 in a period after the time point t.sub.b, as shown in a graph of FIG. 1A with the ordinate representing the opening degree of throttle .theta. and the abscissa representing time t, a voltage V.sub.Q obtained from the air flow sensor of a hot wire type as a determination output for the intake air mass flow may varies with relatively steep pulsations of a small-scale during the period wherein the opening degree of throttle .theta. is held to be the relatively large degree .theta..sub.2 after the accelerating period from the time point t.sub.a to the time point t.sub.b, as shown in a graph of FIG. 1B with the ordinate representing the voltage V.sub.Q and the abscissa representing time t.
These small-scale pulsations in the voltage V.sub.Q result from the fact that the air flow sensor of a hot wire type is operative to determine sensitively small variations in intake air mass flow in the inlet channel caused due to the loss of the intake air mass flow in the inlet channel or the sucking and exhausting operations of the engine. Then, when the voltage V.sub.Q containing such small-scale pulsations is subjected to differentiation for obtaining the variation rate of the intake air mass flow in the previously proposed accelerating detecting system as mentioned above, relatively large differentiation results which are used for finding the accelerating condition of the engine are produced from the small-scale pulsations in the voltage V.sub.Q, and as a result, a wrong detection of the accelerating condition of the engine is likely to be made when the engine is not actually in the accelerating condition.
Such a problem may be also caused similarly in the case where an air flow sensor of a Karman vortex type is employed in the inlet channel provided to the engine in place of the air flow sensor of a hot wire type.